A bearing is generally defined as a device for positioning one element relative to another in such a manner that relative movement between the elements is possible. The elements have respective bearing surfaces, which are in contact with each other.
Bearings are generally employed in order to absorb loads and/or support one or more elements. The element may be rotating, for example a rotating shaft, or it may be fixed, for example a bridge or the like. A bearing may also be designed to be able to absorb both axial and radial forces. The bearing type should be chosen based on its anticipated application.
If there are large loads in a structure, where there has to be a movement between elements therein and where external influences result in fluctuating loads in the structure and its bearings, slide bearings, for example, may be employed.
The use is known also of various types of devices for supporting a turret on a vessel, for example a Floating Production, Storage and Offloading Vessel (FPSO), where these may be slide bearings, roller bearings or wheel suspension. A vessel of this type can be exposed to substantial wind, current and wave influences.
When harsh wind and wave impact occurs on a FPSO, the turret is pressed against the radial turret bearings. This movement and the vessels hog, sag and ovality/tolerances make it necessary to have some kind of radial flexibility on the wheels of a wheel bearing system. This ensures that the distribution of the radial loads is taken on many wheels, not only overloaded onto one or two wheels. A known design is to mount and spring load wheels, such as described in U.S. Pat. No. 5,860,382. The described structure has a spring-loaded wheel in a box assembly, with a spring rod fixed horizontally and vertically to the box assembly. The outer guiding of the box assembly is done by brackets or slots in the surrounding ship structure, or with large steel sections around the rotatable turret rail. And the spring rod is fastened to a lid that has to be bolted to the surrounding structure. This type of arrangement uses a fine alignment between the box assembly and the spring rod, and also has fine tolerances in the surrounding structure. The radial loads to go through the lid bolts, even when the springs are totally compressed and extreme stemming loads occur.